## infiltration concentration and variable head

A discussion forum for old Hydrus-2D & Meshgen. Happy Posting!
Download PDF document with all topics (February 8, 2008, 1.9MB):
http://www.pc-progress.com//Downloads/F ... on_H2D.pdf
lpeters
Posts: 6
Joined: Mon Nov 15, 2004 10:32 am
Location: Netherlands

### infiltration concentration and variable head

Hello,

I appear to get a strange effect when I am simulating infiltration from a variable head boundary in the presence of an atmospheric boundary. For some reason the concentration of the infiltrating water is zero when no precipitation occurs, and the prescribed value when precipitation does occur. When I have a constant head boundary, the simulation is oke. For the moment, I solved the problem by replacing all zero precipitation values by very small dummy values. Is this a known problem, or do I have some error in my data?

cheers
lies

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA
HYDRUS-2D allows you to enter three concentration values when using time-variable boundary conditions, i.e., cValue1, cValue2, and cValue3. The water flux across the boundary is calculated as q_top=Prec-Evap, and solute flux as the product of q_Top time cValue2 or cValue3. With cValue1 it is different. In that case I want to take into account possible increase of concentration of infiltrating water when evaporation is present at the same time as precipitation. In such case cValue1 is recalculated as follows:

if((Prec-Evap).gt.0.) then
cValue1=Prec/(Prec-Evap)*cValue1
else
cValue1=0.
end if

Thus if Evap is greater than Prec, there is no solute entering the profile, since there is no water entering the profile.

Jirka

emiel
Posts: 4
Joined: Mon Mar 06, 2017 12:58 pm
Location: Netherlands

### Re: infiltration concentration and variable head

Hello,

I have a question on the time-variable boundary conditions for solute fluxes (i.e. cValue1, cValue2 and cValue3). I am trying to simulate pesticide transport: from the moment the pesticides are contributed to the land, till the outflow of the pesticides through drains.

I have made a model with on top a time-variable atmospheric boundary conditions and a time-variable solute boundary conditions (cValue1, mg/cm3). The solute boundary conditions has the units mg/cm3. How can I change the input (kg/ha), to mg/cm3? In the post above you explain that if Evap is greater than Prec, there is no solute entering te profile. What happens with the solutes? Is it taken to the next timestep? And is it possible to addapt the solute entering the profile, with the known solubility of the solute?

Thanks!

(Update: I posted this in Hydrus 2D, but I am using Hydrus 2D/3D 2.04.0460)

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: infiltration concentration and variable head

The surface flux is calculated as rTop=abs(Evap)-abs(Prec), and thus Precipitation must be larger than Evaporation to get infiltration. For the case that Precipitation is larger than Evaporation, then we adjust concentration in the infiltration water as follows (to preserve the mass balance):

if((Prec-Evap).gt.0.) then
cPrec(jS)=Prec/(Prec-Evap)*cPrec(jS)

where cPrec is the concentration in Precipitation (irrigation).

J.